Technical Abstract:
The Villegas-Glisson Newcastle disease virus strain from the University of Georgia (VG/GA) was isolated from the intestine of healthy turkeys and has been demonstrated to replicate in the respiratory and intestinal tract of chickens. Field experiences have shown that the VG/GA is useful in the control of velogenic-viscerotropic strains which preferentially targets the intestinal tract of the birds. The differential replication pattern that diminishes the damage to the respiratory tract and an improved local immunity represented by increased IgA production in the intestinal tract are the unique features of the vaccine. In order to assess the genomic base of its tissue tropism, a modified primer sequence-independent amplification method was used to obtain the complete nucleotide sequence of the VG/GA strain. The VG/GA genome was compared to full genome Newcastle disease virus (NDV) sequences available in the GenBank. The VG/GA strain groups within the class II, genotype II viruses that correspond to most of the respirotropic vaccine strains used in the poultry industry and differed from lentogenic enterotropic strains that belong to the class II in the genotype I. The composition of the VG/GA strain genes and proteins were compared with those of the LaSota strain, differences were observed at both the nucleotide and amino acid levels. The changes observed in proteins associated with tissue tropism may explain the differential phenotype of the VG/GA. Further studies including the generation of a reverse genetic system for the VG/GA are required to verify the significance of those changes.